i40e/i40evf: fix extension header csum logic

i40e/i40evf: fix extension header csum logic

The hardware design requires that the driver avoid indicating
checksum offload success on some ipv6 frames with extension
headers.

The code needs to just check for the IPV6EXADD bit and if
it is set punt the checksum to the stack.  I don't know why
the code was checking TCP on inner protocol, as that code
doesn't make any sense to me but seems wrong, so remove it.

Change-ID: I10d3aacdbb1819fb60b4b0eb80e6cc67ef2c9599
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-By: Jim Young <jamesx.m.young@intel.com>
Tested-by: Sibai Li <sibai.li@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>